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I have an 08 TL type S with about 90k on it. When I first purchased the car at 80k, the heater only blew hot air when the temperature was set to 25 degrees celsius. Now, after driving it, I have to set the heater to 29 degrees to blow hot air. I have not bled the coolant of air or done anything else to the cooling system. AC still works well, the fans still work, just the temperature control seems inaccurate.
What could be the issue? Is it potentially the heater core getting clogged? I'm hoping its a cheap fix that I can do myself.
it's the "HVAC mixer"
it's a little black box underneath the dash. it has an electronic arm that moves when the heater gets set to a certain temp.
i believe the electronics die.
the last time i checked for them at the dealer, it was back ordered and had no time frame available to purchase.
you can buy used tho...although, it's a gamble as the electronics can die again
If the heater core were clogged, it would be doubtful you would ever get true hot air.
So two things come to mind...one of which has already been mentioned
1.) HVAC Mixer
2.) HCV - Heater Control Valve
One of them is possibly sticking and not opening/closing smoothly. These are the two things I "should" be looking at in my own car to resolve my HVAC issues. My A/C is ice cold and my heat is hot as hell. There just isn't any in between. I have to go to "Lo" or "Hi" to get any temperature change. Anything in between are just random numbers that have little to no bearing on what temperature the air is that comes out of the vents.
1.) Somewhere under the dash....as previously stated...I have yet to take on this challenge myself so I haven't done all of the research.
2.) Engine bay, on the firewall roughly off center. Pull the covers behind the strut tower brace...it is hiding back there.
How to test each? This again is the research project of searching the forums to find the threads were lots of the details are already documented. Pretty sure both of them will come down to making temp changes on the HVAC controls and watching for movement of the system.
1.) Somewhere under the dash....as previously stated...I have yet to take on this challenge myself so I haven't done all of the research.
2.) Engine bay, on the firewall roughly off center. Pull the covers behind the strut tower brace...it is hiding back there.
How to test each? This again is the research project of searching the forums to find the threads were lots of the details are already documented. Pretty sure both of them will come down to making temp changes on the HVAC controls and watching for movement of the system.
Can anyone else chime in an suggest where the first item is?
On my 07-TL-S i tend to either keep it at Hi/Lo or 23C as an inbetween. On Hi there is no mixing and its just hot air from the system. On Lo once again there is no mixing and its cold/ac. Personally if Hi and Lo work properly, and something in between 23/24 works i'd be content.
Originally Posted by rohan08TL
Can anyone else chime in an suggest where the first item is?
The climate control unit controls the blower motor and supplies a 5 V DC reference voltage to the driver's air mix control motor and the front passenger's air mix control motor.
The air mix and mode control motors all receive inputs from the climate control unit. The driver's and front passenger's air mix motors regulate the mixture of cold and hot air by varying the position of the heater-evaporator doors. The driver's and front passenger's mode control motors control the direction and volume of outlet air. Use the MODE buttons to select the vents the air flows from, although some air will flow from the dashboard corner vents in all modes. Each time the MODE buttons are pressed, the display shows each of the modes selected. Press the buttons four times to see all of the modes. The climate control unit grounds the air mix control motors and the mode control motors.
The recirculation control motor receives battery voltage through fuse 30 (in the under-dash fuse/relay box) with the ignition switch in ON (II). The recirculation control motor regulates the position of the fresh/recirc door and is controlled by two position inputs from the climate control unit ("RECIRCULATE" and "FRESH").
Last edited by 001Stunna; May 5, 2017 at 07:13 PM.
On my 07-TL-S i tend to either keep it at Hi/Lo or 23C as an inbetween. On Hi there is no mixing and its just hot air from the system. On Lo once again there is no mixing and its cold/ac. Personally if Hi and Lo work properly, and something in between 23/24 works i'd be content.
Do I need to replace the air mix control motor for both pssenger and driver?
which side in the diagram is the front of the car and the rear?
I posted this earlier about my heater not working until I set the temperature in my car to 31degrees. Over time, it has gotten worse progressively, as I drove the car that minimum temperature increased first to 26, and now all the way to 31.
The coolant level is fine, the water pump has been replaced, I believe there is no air in the system as the car cools fine, the temperature gauge e don't bounce around. The car does take really long to cool down after it is turned off but I'm pretty sure that's unrelated.
Last time I posted this, people suggested either the HVAC mixer or the heater control valve. Today, I took the cable off the heater control valve and manually adjusted the opening. I set the temperature to 31 degrees and manually opened and closed the valve. When the valve was open, it blew hot air and when it was closed, it blew room temperature/cold When I decreased the temperature below 31, no matter whether I opened or closed the valve, it blew the room temperature/cold air. When I was doing the diagnosis, I also noticed, the vent on top of the navi screen on the drivers side wasn't blowing any air.
This makes me think it's not the heater control valve itself as I manually opened and closed it and nothing changed at the lower temperatures (below 31 degrees Celsius). This makes me think its the HVAC mixer.
What is everyone's thoughts on this and can anyone point me in the right direction? How do I go about replacing the HVAC mixer? Which one in the doagram above is the mixer?
With the HCV taken out of the picture based upon your testing, that pretty much leaves the Air Mix motors or the temp sensor as the culprit. Can you confirm the temp behavior is the same on both sides of the car? You are focused on heat, how does your A/C behave? On my '05, my driver's side is generally warmer than the passenger side on heat and A/C. And my heat and A/C both are either ON or OFF...not much in between on temps...I am guessing either my blend doors are dorked, or my HCV isn't working quite right.
Also, the lack of air out of the driver's center vent leads me to think there may be issues with your Driver's mode motor/door as well.
With the HCV taken out of the picture based upon your testing, that pretty much leaves the Air Mix motors or the temp sensor as the culprit. Can you confirm the temp behavior is the same on both sides of the car? You are focused on heat, how does your A/C behave? On my '05, my driver's side is generally warmer than the passenger side on heat and A/C. And my heat and A/C both are either ON or OFF...not much in between on temps...I am guessing either my blend doors are dorked, or my HCV isn't working quite right.
Also, the lack of air out of the driver's center vent leads me to think there may be issues with your Driver's mode motor/door as well.
After I hit thw recirculate button for the 5th time, both driver and passenger come on at high with a low fan speed, then driver and passenger at the lowest temperature setting at full fan speed and then the diagnostic stops.
Is the diagnostic supposed to keep running? Shat is supposed to happen?
With the HCV taken out of the picture based upon your testing, that pretty much leaves the Air Mix motors or the temp sensor as the culprit. Can you confirm the temp behavior is the same on both sides of the car? You are focused on heat, how does your A/C behave? On my '05, my driver's side is generally warmer than the passenger side on heat and A/C. And my heat and A/C both are either ON or OFF...not much in between on temps...I am guessing either my blend doors are dorked, or my HCV isn't working quite right.
Also, the lack of air out of the driver's center vent leads me to think there may be issues with your Driver's mode motor/door as well.
I just tried this. The temperature behaviour is the same on both sides of the car with heat and AC. As well, the AC is blowing strong out of the drivers side center vent.
